伴随2000年9月30日sawtooth事件地磁变化和电流楔特征研究

为了解极光电集流在sawtooth事件期间的响应情形,本文利用北半球高纬地磁台站的磁场数据,建立了以球元基本电流系反演法求得大尺度电离层水平等效电流系分布的方法,以此研究了2000年9月30日同步轨道LANL卫星观测到的sawtooth事件期间极光电集流的变化.本文将sawtooth注入事件后极区电离层夜侧西向电集流增长的特征,与中低纬地基磁场北向分量正弯扰的特征做比较分析.两者的观测结果都表明在本sawtooth注入事件期间有电流楔的形成,且电流楔约有11 h磁地方时(MLT)的宽度.此外,中低纬磁弯扰达到最大扰动值的时间一般比高纬电集流达到最大扰动值的时间长,说明影响中低纬磁弯扰变化的电流源较丰富.

Escape Rate in the Bistable Sawtooth System Driven by Correlated Multiplicative and Additive White Noises

We study the escape problem of a bistable sawtooth system driven by correlated multiplicative and additive white noises.Exact analytic representation of the relative escape rate is obtained.Some novel phenomena are found from the calculation result;“suppression platform”appears in the relative escape rate when the noise correlation coefficientλis positive.Moreover,for small positive values ofλ,the relative escape rate exhibits“suppression platform”and then“resonant activation”with the increasing noise strength ratio R.

Improved performance of near UV light-emitting diodes with a composition-graded p-AlGaN irregular sawtooth electron-blocking layer

We investigate the performances of the near-ultraviolet（about 350 nm-360 nm） light-emitting diodes（LEDs） each with specifically designed irregular sawtooth electron blocking layer（EBL） by using the APSYS simulation program.The internal quantum efficiencies（IQEs）,light output powers,carrier concentrations in the quantum wells,energy-band diagrams,and electrostatic fields are analyzed carefully.The results indicate that the LEDs with composition-graded pAlxGa1-xN irregular sawtooth EBLs have better performances than their counterparts with stationary component p-AlGaN EBLs.The improvements can be attributed to the improved polarization field in EBL and active region as well as the alleviation of band bending in the EBL/p-AlGaN interface,which results in less electron leakage and better hole injection efficiency,thus reducing efficiency droop and enhancing the radiative recombination rate.

Study of sawtooth oscillations on the HT-7 tokamak using 2D tomography of soft x-ray signal

It is the first time so far as we know that two arrays of multi-channel soft x-ray detectors are used to generate twodimensional （2D） images of sawtooth oscillation on the HT-7 tokamak using the Fourier-Bessel harmonic reconstruction method, and using the singular value decomposition to analyse the data from soft x-ray cameras. By these two arrays, 2D image reconstruction of soft x-ray emissivity can be obtained without assumption of plasma rigid rotation. Tomographic reconstruction of the m=1 mode structure is obtained during the precursor oscillation of the sawtooth crash. The crescent-shaped mode structure appearing on the contour map of the soft x-ray emissivity is consistent with the quasiinterchange mode. The characteristics of the m=1/n=1 mode structure observed in the soft x-ray tomography are as follows： the magnetic surface is made up of the crescent-shaped “hot core” and the circular “cold bubble”. The structure of the magnetic surface rotates in the direction of the electron diamagnetic drift and the rotation frequency is the oscillation frequency of soft x-ray signals.

Sawtooth Activity in Ohmically Heated Plasma on HT-7 Tokamak

Sawtooth activity on HT-7 tokamak has been investigated experimentally mainly by using soft x-ray diode array and magnetic probes. Their behaviors and occurrences are correlated closely to the discharge conditions: the electron density Ne, the electron temperature Te, the safety factor qa on plasma boundary and wall condition etc. When central line-averaged electron density Ne(0) is over 2.0×1013cm-3 , major sawtooth activity emerges with a period of up to 6.5 ms and a fluctuation amplitude of up to 2-30 % of SXR radiation signal. In some cases such as the safety factor between 4.2-4.7 and Zeff=3.0-6.0, a monster sawtooth activity often emerges without apparent deterioration of plasma confinement and without major disruption. During these events, abundant MHD phenomena are observed including partial sawtooth oscillations. In this paper, the observed sawtooth behaviors and their dependence on the and their dependence density Ne and wall condition in ohmically heated plasma are introduced, the results are discussed and presented.

Sawtooth and dune auroras simultaneously driven by waves around the plasmapause

The dune aurora,at a scale of~30 kilometers,was reported recently using ground camera.The small-scale dune aurora occurs on the duskside and exhibits a monochromatic oscillation in the auroral emission,implying fundamental energy conversions.However,whether the dune auroras correspond to atmospheric waves or are associated with magnetospheric dynamics should be determined.This paper reports a dune aurora that occurred during a storm;further,we demonstrate that it was the substructure of the sawtooth aurora that was generated by plasmapause surface waves.Conjugate observations in the magnetospheric source region suggest that the exohiss waves,which are periodically modulated by the plasmapause surface wave-excited ultralow frequency wave,might be responsible for the generation of the dune aurora.Most reported dune aurora events have occurred simultaneously with sawtooth auroras,suggesting that both are plasmapause-driven cross-scale auroral structures.

Compound sawtooth in EAST LHCD plasma:An experimental study

A compound sawtooth with an incomplete relaxation was observed in EAST＇s lower hybrid current drive （LHCD） plasma. The sub-crash phase of the compound sawtooth corresponds to a longer-lasting and slower-growing 1/1 mode. Based on the two-dimensional （2D） SXR tomography, the time-dependent 2D image of a compound sawtooth crash is obtained. The island produced during a resistive internal kink mode is observed in the all crash phases of the compound sawtooth. The destabilization of 1/I long-lasting saturated 1/1 mode is related to the current driven by the LHCD near the q = 1 surface.

Sawtooth Control Experiments on HT-7 and EAST Tokamak

Sawtooth control experiments were performed on HT-7 with a limiter configuration and on the Experimental Advanced Superconducting Tokamak （EAST） with a double null con- figuration. The sawtooth period can be modified by lower hybrid wave （LHW） and ion cyclotron resonance frequency （ICRF）. Different sawtooth behavior was observed with the same plasma density, LHW power but different plasma currents on HT-7. There was a dwell time between LHW added and the sawtooth stabilization on HT-7 while the sawtooth stabilization immediately happened when LHW power was injected on EAST. The possible mechanism of the sawtooth control is discussed in this paper. All the experimental results have proved that power deposition of the radio frequency （RF） should be the key factor for sawtooth control.

Sawtooth Activities During Impurity Injection by Laser Blow-off in HL-2A

In order to study impurity transport and their progression in the plasma, small amount of high-Z impurities were injected into HL-2A ohmic heated plasmas by laser blow-off and traced with good spatial temporal resolution by a soft X-ray camera. An analysis of the evolution of the impurities＇ radiation distribution in the plasma revealed that impurity transport in the central region was profoundly different from that outside of it. It was found that the sawteeth tended to be inverted on the central soft X-ray chord signals after the impurity injection and the soft X- ray profiles exhibited discontinuities during the movement of the impurities in the plasma central region. Detailed 2D visualization of the evolution of impurities＇ radiation using computer tomography has provided further understanding of the properties of impurity transport in the HL-2A plasma.

Preliminary Results of Sawtooth Behaviour and Electron Heat Transport During ECRH Experiment on HL-2A

An electron cyclotron resonance heating （ECRH） system with a maximum output power of 1 MW, a frequency of 68 GHz and a duration of ls was operated on HL-2A tokamak. The temperature profile control and the sawtooth behaviour during ECRH experiments are investigated. ‘Density pumpout＇ during on-axis ECRH is analysed. Features of confinement and electron heat transport during ECRH are studied.

Study of Inverted Sawtooth Activities in EAST Plasma

On the EAST tokamak, during whole off-axis LHCD （low hybrid current drive） limiter discharge, inverted sawteeth oscillations on the SXR （soft X-ray camera） signals appear continuously, and no positive sawtooth is observed. It is thought that this phenomenon is caused by the curvature pinch, though it could partly be explained by the electron temperature profile observed on the PHA （soft X-ray pulse height analyzer） system. The off-axis LHCD and Ohmic heating generate a non-monotonic q profile. According to the curvature pinch effect, this q profile leads to a special electron density profile that has a valley ring. The non-monotonic q profile and the special electron density profile lead to this interesting phenomenon.

Observation of the poloidally asymmetrical density perturbation of sawtooth collapse on J-TEXT

The detailed density perturbations provided by the advanced polarimeter-interferometer system(Polaris) during sawtooth collapse on the Joint Texas Experimental Tokamak(J-TEXT) are reported in this article.During a sawtooth collapse and the crash of plasma pressure at the center,it is found that the increase in density in the region between the inversion radius and mixing radius is poloidally asymmetrical,while the increase in temperature is poloidally symmetrical.The poloidal location where the density increases is dependent on the phase of the precursory m/n=1/1 kink mode.It is always out of phase with the hot core of the m/n=1/1 mode.The behaviors of density perturbations during sawtooth collapse observed in J-TEXT are beyond the expectations of the standard model,and this can shed new light on the understanding of sawtooth collapse.

Sawtooth-like oscillations and steady states caused by the m/n=2/1 double tearing mode

The sawtooth-like oscillations resulting from the m/n=2/1 double tearing mode(DTM)are numerically investigated through the three-dimensional,toroidal,nonlinear resistive-MHD code(CLT).We find that the nonlinear evolution of the m/n=2/1 DTM can lead to sawtooth-like oscillations,which are similar to those driven by the kink mode.The perpendicular thermal conductivity and the external heating rate can significantly alter the behaviors of the DTM driven sawtooth-like oscillations.With a high perpendicular thermal conductivity,the system quickly evolves into a steady state with m/n=2/1 magnetic islands and helical flow.However,with a low perpendicular thermal conductivity,the system tends to exhibit sawtooth-like oscillations.With a sufficiently high or low heating rate,the system exhibits sawtooth-like oscillations,while with an intermediate heating rate,the system quickly evolves into a steady state.At the steady state,there exist the non-axisymmetric magnetic field and strong radial flow,and both are with helicity of m/n=2/1.Like the steady state with m/n=1/1 radial flow,which is beneficial for preventing the helium ash accumulation in the core,the steady state with m/n=2/1 radial flow might also be a good candidate for the advanced steady state operations in future fusion reactors.We also find that the behaviors of the sawtooth-like oscillations are almost independent of tokamak geometry,which implies that the steady state with saturated m/n=2/1 islands might exist in different tokamaks.

Monster Sawtooth Activity in Ohmically Heated HT-7 Plasma

Experimental properties of monster sawtooth activities in ohmic HT-7 plasma are presented in this paper. The monster sawtooth activities belong to global fluctuations and are characterized with a series of large core collapses on SXR intensity traces with a long period, a large amplitude fluctuation and a large inversion radius. However, they emerge without apparent deterioration of plasma confinement and without major plasma disruption. During the events, long partial sawtooth collapses and abundant MHD phenomena are also observed.

Effects of sawtooth heat pulses on edge flows and turbulence in a tokamak plasma

Enhancements of edge zonal flows,radial electric fields,and turbulence are observed in electron cyclotron resonance heating-heated plasmas(Zhao et al 2013 Nucl.Fusion 53083011).In this paper,the effects of sawtooth heat pulses on flows and turbulence are presented.These experiments are performed using multiple Langmuir probe arrays in the edge plasmas of the HL-2A tokamak.The edge zonal flows,radial electric fields,and turbulence are all enhanced by sawteeth.Propagation of the zonal flow and turbulence intensities is also observed.The delay time of the maximal intensity of the electric fields,zonal flows,and turbulence with respect to the sawtooth crashes is estimated as~1 ms and comparable to that of the sawtooth-triggered intermediate phases.Not only the zonal flows but also the radial electric fields lag behind the turbulence.Furthermore,the intensities of both the zonal flows and electric fields nearly linearly increase/decrease with the increase/decrease of the turbulence intensity.A double-source predator-prey model analysis suggests that a relatively strong turbulence source may contribute to the dominant zonal flow formation during sawtooth cycles.

Flow of Generalized Burgers’ Fluid Induced by Sawtooth Pulses Stress with Quadratic Edges

This paper presents the unsteady magnetohydrodynamic (MHD) flow of a generalized Burgers’ fluid between two side walls perpendicular to a plate. The flow is generated from rest at time ?induced by stress applied on the bottom plate. The stress is assumed to be like sawtooth pulses with quadratic edges. The solutions obtained by means of the Laplace, and Fourier cosine and sine transforms are presented as a sum between the corresponding Newtonian and non-Newtonian contributions. Graphs are sketched for various parameters of interest.

The Diffusion Coefficient Using Sawtooth Oscillation in IR-T1 Tokamak

The investigation of runaway electrons is expanded by different methods. The aim of this study is to show sawtooth oscillations of hard x-ray emission and with the help of sawtooth oscillations to obtain radial diffusion coefficient and magnetic fluctuations. In the same way, the hard x-ray spectral evaluation is compared in several time intervals and it is shown that during discharge, the energy of the runaway electrons is less than 200？keV. Also, for typical plasmas, population of runaway electrons is measured at seven time intervals of 5ms and temporal evaluation of runaway electron mean energy. The sawtooth-like shape is observed in the hard x-ray range （10–1000？keV）. By the sawtooth oscillation method, the RE diffusion coefficient in radial transport in the IR-T1 plasma is Dr～0.5Dr～0.5m^2s^-1. The magnetic field fluctuation due to magnetic diffusion DmDm is given as br/Bt～10^-4.

Soft X-ray Tomography and Sawtooth Oscillations during IBW in HT-7 Tokamak

Tomographic reconstructions of soft x-ray emissivity in the HT-7 tokamak have been obtained using 86 miniature soft-x-ray detectors. Because there are two-detector arrays which are distributed in horizontal and vertical directions on one poloidal plane, two-dimensional images of x-ray emissivity are obtained without having resort to a rotational model. The algorithm of Fourier-Bessel expansion was employed. The data analysed so far have been used principally to study MHD instabilities, and the illustrative examples of the sawtooth crash in IBW-heated plasma are described.

前锯肌平面阻滞对胸腔镜肺癌根治术后肺功能和免疫功能的影响

目的比较超声引导下前锯肌平面阻滞(SAPB)对胸腔镜下肺癌根治术后患者肺功能和免疫功能的影响。方法收集2020年1月至2023年2月在河北北方学院附属第一医院接受胸腔镜肺癌手术的135例患者,根据随机数字表法分为3组:对照组(n=45)仅接受全身麻醉,罗哌卡因组(n=45)在接受罗哌卡因局部浸润麻醉,SAPB组(n=45)接受SAPB。比较3组患者临床数据、手术资料,使用视觉模拟量表评分法(VAS)评估患者在静息和咳嗽时的疼痛情况,并收集围术期并发症发生情况。使用流式细胞仪和相应试剂检测患者术前、术后血清中T淋巴细胞亚群的水平、血清癌胚抗原(CEA)、癌胚抗原(CA)125、细胞角蛋白19片段21-1(CYFRA21-1)和神经元特异性烯醇化酶(NSE)水平。结果罗哌卡因组和SAPB组术中瑞芬太尼用量均低于对照组,首次按压患者自控镇痛(PCA)泵时间均晚于对照组,术后48小时内PCA泵按压次数均少于对照组,差异均有统计学意义(P<0.05)。3组患者不同时间点的静息、咳嗽VAS评分、CD3^(+)、CD4^(+)、CD8^(+)和CD4^(+)/CD8^(+)水平差异有统计学意义(P均<0.05)。术后24小时罗哌卡因组和SAPB组的CEA、CA125、CYFRA21-1和NSE水平均低于对照组(P均<0.05)。3组患者不良反应发生率分别为15.56%、4.44%和4.44%,差异无统计学意义(χ^(2)=4.949,P=0.084)。结论SAPB在提高胸腔镜下肺癌根治术后镇痛效果的同时,对调节患者机体免疫功能,降低血清肿瘤标志物水平有益。

板蓝根收获机锯齿式挖掘装置设计与试验

【目的】设计板蓝根收获机锯齿式挖掘装置,为提高我国板蓝根的机械化收获水平提供支持。【方法】依据板蓝根四垄一行的种植模式,设计了锯齿式挖掘装置及其关键部件,通过对挖掘装置挖掘过程的分析,确定了影响挖掘阻力和土壤破碎率的关键参数。采用EDEM离散元仿真方法,以挖掘阻力和土壤破碎率为评价指标,对铲面倾角、铲刃角、铲尖长度进行三因素三水平仿真试验并建立回归模型,再采用多目标变量优化方法,运用Design-Expert 8.0.6对回归模型进行优化求解以确定最佳结构参数组合,对最佳铲面倾角、铲刃角和铲尖长度组合的圆整值进行虚拟仿真试验验证,在仿真基础上以挖掘阻力和根茎损伤率为评价指标,与现有的三角铲式挖掘装置进行了田间对比。【结果】受力分析表明,影响板蓝根收获机锯齿式挖掘装置挖掘性能的主要结构参数为铲面倾角、铲刃角、铲尖长度及铲体宽度,依据板蓝根种植模式确定铲体宽度最佳值为600 mm。仿真分析表明,锯齿式挖掘装置最佳作业参数为铲面倾角16.68°,铲刃角53.05°,铲尖长度376.75 mm,理论挖掘阻力5.17 kN,土壤破碎率65.20%。利用最佳作业参数的圆整值(铲面倾角17°,铲刃角53°,铲尖长度377 mm)进行虚拟仿真验证,其挖掘阻力为5.19 kN,土壤破碎率为66.03%。田间对比试验表明,相对于三角铲式挖掘装置,锯齿式挖掘装置的挖掘阻力降低了8.41%,根茎损伤率降低了13.43%,2个评价指标均优于三角铲式挖掘装置。【结论】板蓝根收获机锯齿式挖掘装置的铲面倾角为17°,铲刃角为53°,铲尖长度为377 mm时,可以满足板蓝根收获作业的工作要求。